Update values of existing template variables and add new variabels to the existing set of variables for all devices.

Example:

Existing variables:
{"AB0011111": {"_sys_serial": "AB0011111", "_sys_lan_mac": "11:12:AA:13:14:BB", "SSID_A": "Z-Employee"},
"AB0022222": {"_sys_serial": "AB0022222", "_sys_lan_mac": "21:22:AA:23:24:BB", "vc_name": "Instant-23:24:BB"}}

Variables provided in this request body:
{"AB0011111": {"_sys_serial": "AB0011111", "_sys_lan_mac": "11:12:AA:13:14:BB", "SSID_A": "X-Employee", "vc_name": "Instant-23:24:BB"}},
"AB0022222": {"_sys_serial": "AB0022222", "_sys_lan_mac": "21:22:AA:23:24:BB", "vc_name": "Instant-23:24:AA", "SSID_A": "Z-Employee"}}

Final output variables:
{"AB0011111": {"_sys_serial": "AB0011111", "_sys_lan_mac": "11:12:AA:13:14:BB", "SSID_A": "X-Employee", "vc_name": "Instant-23:24:BB"}},
"AB0022222": {"_sys_serial": "AB0022222", "_sys_lan_mac": "21:22:AA:23:24:BB", "vc_name": "Instant-23:24:AA", "SSID_A": "Z-Employee"}}

In Final output variables, for "AB0011111" device "SSID_A" is updated and "vc_name" is created
and for "AB0022222" device "vc_name" is updated and "SSID_A" is created.